The invention relates to a gas detector having a gas sensor for sensing a change in the concentration of a specific gas in air, and a case for housing the gas sensor.
Some gas detectors have a gas sensor incorporated in a case and detect a gas included in air flowing through an air flow channel formed in the case.
For example, a vehicle gas detector described in JP-A-8-192617 has a case. An air inlet port is formed in a lower portion of a front surface of the gas detector, and an air outlet port is formed in an upper portion of a rear surface of the detector. An air flow channel is formed in the case so as to extend upward from a substantially lower position. The gas sensor detects the concentration of a gas in the air flowing through the air flow channel. In the vehicle gas detector, the air having flowed into the air inlet port migrates upward along the air flow channel, whilst water droplets having flowed into the air inlet port in conjunction with the air adhere to a wall surface and migrate downward under the influence of gravity. The water droplets are then discharged out of the air inlet port.
In general, as a larger quantity of air flows through the air flow channel, the air present in the flow channel is replaced quickly, whereupon the response of the gas sensor becomes faster.
However, in relation to the vehicle gas detector, when an attempt is made to cause a larger quantity of air to flow into the detector by means of increasing the size of the air inlet port for taking in as large quantity of air as possible with a view toward increasing the response of the gas sensor, or by means of selecting the mount position of the gas detector, a large quantity of water droplets flow into the air flow channel in conjunction with air. In such a case, in the vehicle gas detector, air migrates upward along the air flow channel, and downward migration of water is hindered by flow of air. Thus, water cannot be discharged appropriately. Accordingly, water is accumulated within the air flow channel, thereby narrowing the air flow channel and hindering circulation of air. Thus, in some cases a drop in the response of the gas sensor has arisen. Moreover, if water is accumulated in the vicinity of the gas sensor, water may enter the gas sensor.
The invention has been conceived in view of the problems and is aimed at providing a gas detector which can discharge water appropriately even if air has flowed into the detector along with water droplets.